1. Field of the Invention
This invention relates to automated test equipment for testing integrated circuits, and, more particularly, to programmable interface boards used between the automated test equipment (ATE) and an integrated circuit device under test (DUT).
2. Prior Art
Testing of integrated circuits has become much more difficult for a number of reasons. One reason is that the integrated circuits now being produced and tested are much faster and more complex than previous integrated circuits. This means that the signals for testing these integrated circuits operate at higher frequencies and consequently require short, impedance-controlled signal lines to minimize signal delay, mistiming and distortion. Another reason is that many more application specific integrated circuits (ASICs) are now being produced, each one of which has different electrical requirements and configurations for the various pins or leadless terminals. Because ASICs usually are produced in low production volume and because of the large variety of ASIC products now being offered, traditional methods for testing high volume integrated circuits using dedicated test setups are not particularly applicable to testing a large variety of low volume ASICs.
Previously, a conventional interface board has been used to interconnect the ATE equipment and the DUT. The DUT was fixed in a holder mounted on a DUT printed circuit board. The DUT board was then mounted to and electrically connected to the interface board. To accommodate various electrical test signal requirements for a particular DUT, electrical connections between the interface board and the individual pins of the socket are sometimes made with wires which are wirewrapped onto the socket pins. Additional electrical components, such as bypass capacitors and pull-up resistors, are connected and disconnected between various pins of the socket by hand soldering, and unsoldering, as required. For production runs, even though they may be relatively low-volume production runs, this technique is time consuming and sometimes unreliable. Because they are designed to be used in a production environment, industrial grade DUT boards are relatively expensive and consequently the connections are often reworked to accommodate various different ASIC products. As a consequence of being reworked several times, these expensive boards often become unreliable and must be discarded.
A conventional interface board is typically an 18-inch diameter, relatively large, circular-shaped, multi-layer printed circuit board which has a smaller 6-inch diameter DUT board mounted in its center. The interface board serves as an interface between the ATE signals and, perhaps, several hundred or more terminals or pins of a DUT. An interface board has several hundred or more signal lines which radiate from the DUT board in the center of the interface board to the periphery of the interface board. An interface board usually is a multilayer printed circuit board with various signal traces and power and ground planes.
One commonly used interface board is a Switch Programmable Interface Board which uses a combination of relays and toggle switches to connect the terminal pins of a DUT mounted on a DUT board to the various ATE test signals and power supplies. Each of the DUT pins is connected to one relay and to one 3-way toggle switch. Operation of the relays is controlled by the software of an ATE test program. The toggle switches for each pin are manually set as required to provide power, ground, or no-contact. The very large number of relays and toggle switches (one set for each of the several hundred or more DUT pins) are positioned on the periphery of the interface board. Because each relay is electronically controlled by the ATE test program software, each relay requires a control line. As the number of pins on DUTs has increased, the number and complexity of signal lines and relay control lines on conventional interface boards has also increased. Performance at higher frequencies has also been affected due to the increased number of lines and due to inductance and capacitive pickup problems associated with long signal leads. The increased number of pins also increases problems associated with those interconnections between the interface board and the pins of the DUT socket which require reusable wirewrap and solder connections.
FIG. 1A shows a circuit diagram for configuring the connections of a Switch Programmable Performance Board. The pin electronics PE circuit of an ATE test system is connected to a DUT terminal or pin. The DUT terminal is also connected to one contact terminal of a relay. The other contact terminal of the relay is connected to one terminal of a resistor R with its other terminal connected to a DPS2 terminal. The other contact terminal of the relay is connected to the output terminal of a three-way toggle switch. The toggle switch selectably connects power supplies VDD, VSS, or no-contact (NC) to the relay contact.
FIG. 1B shows an alternative circuit diagram for configuring a pin of a Switch Programmable Interface Board. A DUT terminal is directly connected to the output terminal of a three-way toggle switch. Power, ground and no-contact (NC) are selectably connected to the DUT terminal. A relay is closed to connect a PE circuit to the DUT terminal.
U.S. Pat. No. 4,354,268 discloses an "intelligent" head which uses relay contacts to connect the pin electronics board of a computer-controlled automated test system to a DUT. The relay contacts selectively connect either the pin electronics or special test functions from the test head to the DUT.
With the increased DUT pincounts and higher test frequencies being used, using relays and toggle switches increases programming complexity and requires large amounts of area on the interface board to mount those components, one relay and toggle switch for each signal line. The relays and toggle switches are mounted on the outer edge of an interface board and the DUT is mounted in the center of the interface board. Because of the large number of relays and toggle switches and because they are located on the periphery of the interface board, it is necessary to have long interconnecting conductors with increased inductance and interference pickup. Consequently, it is desirable to minimize or to altogether eliminate relays and toggle switches for testing an integrated circuit having a very large number of terminal pins.